Pediatric Soft Tissue Tumors

Abstract

Soft tissue masses are very common and have an extraordinarily wide range of possible etiologies in pediatric age group. The World Health Organization (WHO) has classified soft tissue tumors into nine distinct categories. Each category is further subdivided into benign, intermediate (locally aggressive), and malignant types. These categories are as follows: Adipocytic tumors; Muscle tissue tumors; Peripheral nerve sheath tumors; Fibrohistiocytic tumors; Fibroblastic - myofibroblastic tumors; Vascular tumors; Tumors of bone and cartilage; Ewing sarcoma family of tumors; Tumors of uncertain differentiation. Malignant soft tissue tumors (sarcomas) are relatively rare, representing less than 1% of all malignancies. Soft tissue sarcomas are associated with high mortality rates. For many soft tissue masses, it is quite difficult to distinguish between benign and malignant solely based on imaging. Some soft tissue sarcomas can appear deceptively well-defined, with smooth margins and homogeneous signal intensity. If a lesion does not have characteristics specific to a particular benign entity, it should be considered potentially malignant. Superficial soft tissue masses larger than 5 cm have a 10% chance of being sarcomas. Estimating the grade of a soft tissue sarcoma using imaging alone is unreliable. The presence of large, necrotic, and infiltrative masses supports a high-grade lesion. However, high-grade lesions can also appear small, homogeneous, and well-capsulated. Most soft tissue tumors exhibit non-specific, heterogeneous signal intensity characteristics on both T1-weighted (T1W) and fluid-sensitive MRI sequences. However, certain tissue signal types can help indicate a specific tumor type. Adipose tumors contain fatty tissue with high signal intensity on T1W images, and these fatty areas are seen as low signal intensity on fat-suppressed (FS) sequences. Fibroblastic tumors often contain areas with intermediate or low signal intensity on both T1W and fluid-sensitive MRI sequences. Fibrohistiocytic tumors frequently exhibit heterogeneous signal intensity characteristics. The presence of a mass in a typical location can also aid in suggesting a specific diagnosis.